Microbiological surveillance and parenteral antibiotic use: RESULTS
There were 759 admissions to the CrCU during the study. One-third of patients were admitted from the emergency department, 32% of patients came from the operating room and 35% were transferred to the CrCU from another ward or hospital. A total of 258 (32%) patients received parenteral antimicrobial therapy during their CrCU stay, including 75 medical, 105 surgical and 78 trauma patients. There were 340 courses of antibiotics administered; 226 were for treatment of infection and 114 were for surgical prophylaxis. The average duration of antimicrobial therapy for all patients included in the audit was 6.7 days (range one to 54 days). The most frequently prescribed antibiotic was cefazolin (47% of patients, 1098 g total use), followed by gentamicin (33%, 141 g), ceftriaxone (20%, 255 g), metronidazole (19%, 209 g), clindamycin (19%, 459 g) (Dalacin C, Pharmacia & Upjohn Inc, Mississauga, Ontario), cloxacillin (17%, 1913 g), cefuroxime (16%, 323 g) (Zinacef, Glaxo Canada Inc, Toronto, Ontario), vancomycin (15%, 256 g) (Vancocin, Eli Lilly Canada Inc, Scarborough, Ontario), ampicillin (14%, 1028 g) and tobramycin (12%, 81 g) (Table 1). The overall cost of all parenteral antibiotics during the audit was $57,854.35, which represented 18% of the total drug budget for the CrCU for that year.
The average length of stay for patients receiving antibiotics (10.7±14.7 days) was significantly higher than the length of stay of all patients admitted to the CrCU (4.7±8.0 days) during this period (P<0.01). There were 6.3 infections treated with antibiotics/100 patient days during the surveillance period. Of the patients who received antimicrobial therapy, 76% remained in the CrCU for more than 48 h.
When the prophylactic antibiotic use was excluded from the analysis, both the average duration of antibiotic therapy and length of stay increased from 6.7 and 10.7 days to 8.5 (range one to 54) and 13.4 (range one to 146) days, respectively. There did not, however, appear to be a significant change in the most frequently prescribed antibiotics.
The indications for antimicrobial therapy as determined by the attending medical staff in the CrCU are as summarized in Table 2. Several patients had more than one infectious diagnosis. In 34% of the infections treated, no bacterial pathogen was identified. Of the culture results collected, 26.3% were from sterile sites. Of the 30 patients with positive blood cultures, 20 patients had a primary bacteremia without a clearly identified source. In addition to the blood cultures, only 11 other cultures were from sterile sites (eg, cerebrospinal fluid [CSF], tissue biopsies, specimens obtained during surgical procedures). Pneumonia accounted for over one-third of the indications for antimicrobial treatment. Of the pneumonias diagnosed on clinical and radiological features (n=121), microbiological cultures were obtained from endotracheal tube specimens in all but seven; these seven samples were obtained from bronchoalveolar lavage specimens.
The most common organisms isolated from patients with infection were S aureus (25.6%), followed by Pseudomonas aeruginosa (13.5%),Enterococcus species (12.2%),Haemophilus influenzae (10.9%), E coli (10.9%), Enterobacter cloacae (7.7%), other Gram-negative (12.8%) and other Gram-positive organisms (4.5%). In particular, S aureus was the most frequently cultured organism (24.5%) from blood, followed by Enterococcus species (13.2%), Pseudomonas species (11.3%), Staphylococcus epidermidis (9.4%) and Candida albicans (9.4%).
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Of all the S aureus isolates recovered from patients who received parenteral antibiotics in the CrCU, only 5% of the S au- reus strains were methicillin-resistant. There were no VRE or enterococci with high-level aminoglycoside resistance. ES6L or imipenem resistance were not found in Gram-negative bacilli. Twenty-nine per cent of the H influenzae isolates were beta-lactamase positive. E coli was found to have the highest antimicrobial resistance, with 41% resistant to ampicillin, 24% resistant to gentamicin and 6% resistant to cefazolin. ForEcoli isolates collected from across the hospital during 1995 to 1996, the antimicrobial resistance rates were similar for ampicillin and cefazolin but not for gentamicin, for which the rate was only 4%. Within the Enterobacteriaceae, there was no resistance to trimethoprim/sulphamethoxazole; one Klebsiella species was resistant to cefazolin; two Citrobacter freundii were resistant to gentamicin, with one also resistant to cipro- floxacin (Cipro, Bayer Inc, Toronto). Of the Pseudomonas species, 5% were resistant to each of piperacillin (Pipracil, Wyeth Ayerst Canada Inc, Montreal, Quebec), ciprofloxacin and ceftazidime, and none were resistant to the aminoglycosides. One pseudomonal isolate was resistant to both piperacillin and ceftazidime.